Fix building with build-snapshot

This MR addresses some issues when trying to build with build-snapshot as done by the Jenkins jobs:

• avoid debian patches, as the jobs is not configured to use them (see also comments on !1 (merged)), which means:
  • re-enable the libgrassmoor-doc package for real
  • apply the tracker-2.0 dependency changes directly to configure.ac
• disable fatal warnings, since after the rebase new ones have appeared

With this, build-snapshot localhost suceeds in the apertis-v2019dev0-package-builder Docker image, version ce00e4be564f.